Missile Defense: The Myth of Layering

The midcourse Ground-based Missile Defense (GMD) system the United States has deployed in Alaska and California would attempt to intercept missile warheads above the atmosphere. Such “exoatmospheric” defenses are susceptible to a range of countermeasures, such as decoys, that can deny the defense the information it needs to intercept a warhead. Moreover, such countermeasures can be built with technologies that the U.S. intelligence community says are within the reach of any country that can build a long-range missile.

A common response by missile defense advocates to the midcourse countermeasure problem has been “layering.” Specifically, advocates have argued that the countermeasure problem, while real, is not such a worry if the midcourse defense system doesn’t have to work alone, but is aided by other defense layers that could engage long-range missiles early in flight (boost phase) or late in flight (terminal phase) to thin their numbers.

But the layering argument is nonsense.

One problem with the layering argument is this: if you had a layered system and the midcourse layer didn’t add to the defense because of its vulnerability to countermeasures, then why not leave that layer out? That would seem to make more sense than doing the opposite—starting by building the midcourse layer—which is what the U.S. is doing.

The other problem is that these other layers don’t exist, and are not likely to any time soon:

No boost-phase layer
The only boost-phase system the United States is developing is the ill-fated Air-Borne Laser (ABL) program, which hasn’t done well in tests, needs to increase its power by “20 to 30 times,” and has been cut back to a research program. My guess is that one reason for not cancelling the program outright is that the Missile Defense Agency (MDA) would then not be able to point to any additional layer under development. (Another reason for keeping ABL in some form may be its potential anti-satellite capability, which would be operationally much easier for the system than missile defense.)

The administration last year killed the Kinetic Energy Interceptor (KEI) program, which was intended to build a fast interceptor that could be used for boost-phase defense. The head of MDA argued for cancellation noting that the program was well over budget and well behind schedule.

People sometimes mistakenly argue that the Aegis SM-3 interceptor could be used for a boost-phase defense. But this interceptor was not designed for this purpose and does not have the maneuverability required to intercept a maneuvering target like a boosting missile.

No terminal-phase layer
The United States is not developing any terminal defenses against long-range missiles. So it was surprising to see that the illusion of a terminal layer against long-range missiles seems to have confused even people who should know better—for example, Gen. Cartwright, Vice-Chair of the Joint Chiefs of Staff. During questioning after his June 2009 testimony to the Senate Armed Services Committee about missile defense, he was explaining why the U.S. decided it now only needs 30 GMD interceptors when it previously said it needed 44. Cartwright stated:

as we have developed … the terminal capability, with THAAD, Patriot, and SM-3, it has taken some stress off the midcourse.

The midcourse GMD system is intended to shoot down long-range missiles. In his statement, Cartwright is implying that these terminal systems would be able to engage long-range missiles that made it through the midcourse layer.

Yet none of these systems can engage a warhead from a long-range missile during terminal phase, since the warhead would be moving much faster than the warheads these systems are designed to handle. The SM-3 kill vehicle can’t engage at all during terminal phase since it can only operate above the atmosphere.

It’s hard to imagine what Gen. Cartwright was thinking, but to the extent his response is indicative of high-level confusion about the operation of U.S. missile defense systems, it is disturbing.

The fallacy of the layering argument means that the midcourse GMD layer has to be judged on its own, and its vulnerability to countermeasures cannot be ignored.

Ascent-phase layer?
Given all this, it’s not surprising that MDA has recently become interested in a possible new layer, which it hopes might be able to help sometime in the future. This is “ascent phase”—the period shortly after booster burnout when the warhead is still rising. The Obama administration has asked the Defense Science Board to take another look at ascent phase intercept, which it last looked at in 2002.

I’ll discuss ascent phase in a future post. But it doesn’t look like a game-changer.

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David Wright, physicist and co-director of the UCS Global Security Program, is an established expert on the technical aspects of arms control, particularly those related to missile defense systems, missile proliferation, and space weapons.